The annual course of air temperature and near-surface soil temperature in a tropical Savannah environment

Abstract

By harmonic analysis periodic sine-functions were fitted to long-term five-day averages of maximum and minimum temperature of the air at screenheight and of the top 2 cm of bare soil for Katherine, N.T., Australia. A good simulation of the observed annual trend in all four elements was obtained by considering the first two harmonics only. The inclusion of higher harmonics did not lead to any significant improvement. The annual variation of extremes, mean values and ranges of air and soil temperatures and mean annual interrelationships have been studied and the interaction between soil-physical characteristics, rainfall pattern and other weather parameters discussed. A number of characteristic periods could be identified in the interrelationships between the soil and air temperature extremes, which are also climatologically well defined. It was concluded that wetting and drying of the soil are the major factors in determining the thermal regime of the topsoil and hence play an important role in the interrelationships between soil and air temperatures throughout the year. Some agronomic implications of the present climatological outline have been illustrated with reference to characteristic features in the life cycle of the pasture legume Stylosanthes humilis H.B.K., now well established in northern Australia.